The tansy beetle (Chrysolina graminis) is a species of leaf beetle. The common name derives from its main foodplant, Tansy (Tanacetum vulgare), but it can also use other wetland plants such as Gypsywort (Lycopus europaeus) and Water Mint (Mentha aquatica). It measures 7.7–10.5 mm in length and has a characteristic bright metallic green colouration, with pitted elytra and a coppery tinge. In addition to the nominotypical subspecies, which repeats the specific name, C. graminis graminis, there are five further distinct subspecies of Tansy beetle, which, collectively, have a Palearctic distribution, although in the majority of countries where it is found the species is declining. In the United Kingdom it is designated as 'Nationally Rare'. The stronghold population here is located along the banks of the river Ouse in York, North Yorkshire. Other, small, fenland populations exist at Woodwalton Fen and at Welney Wildfowl and Wetlands Trust (WWT) reserve.
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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starts withAll tansy beetles are small, rounded beetles approximately 7–12 mm in length. There are both internal and external morphological differences between the six subspecies.
The tansy beetle has a Palearctic distribution. Evidence from archaeological excavation has shown that its presence in western Europe is confirmed at least as early as the Neolithic period. The beetles may be found on tansy (Tanacetum vulgare) and water mint (Mentha aquatica) in fen land and the banks of rivers with broad floodplains in Britain. Larvae are also recorded from other host plants: Achillea ptarmica (sneezewort) in France and various plants of the genus Artemisia in Russia. Adults and larvae feed on the leaves of their host plants.
In continental Europe, C. graminis is widespread from Scandinavia to the Mediterranean Sea. It may also be found in central Asia and China. In Russia it may be found in the tundra zone from the Polar Urals to the Kolyma River, and in the nearby countries of Kazakhstan, and Mongolia. It is listed as vulnerable in Austria, Denmark, Sweden and Norway, and in Germany it is rare in one district, endangered in another.
Tansy beetles are herbivorous and primarily use tansy (Tanacetum vulgare) as their host plant. The species has, however, also been recorded consuming a wider range of food plants including Lycopus europaeus (gipsywort), Stachys palustris (marsh woundwort), Achillea ptarmica (sneezewort), Mentha aquatica (water mint), Mentha rotundifolia (false apple mint), as well as other species of the genera Chrysanthemum, Scutellaria, and Artemisia. The subspecies C. graminis santonico is associated with Artemisa caerulescens.
The tansy plant naturally contains a number of volatile components including 1,8-cineole, trans-thujone, camphor and myrtenol, with the quantities and proportions of each varying seasonally and from plant to plant. 1,8-cineole is a toxin believed to defend the plant leaves against attacks by herbivores. The tansy beetle is resistant to these chemicals. However, tansy is a repellent to other Chrysomelid beetles. For example, the steam distillate of fresh leaves and flowers of tansy contains high levels of camphor and umbellulone and is strongly repellent to the Colorado potato beetle (Leptinotarsa decemlineata).
Both adults and larvae use the same host plant during their life cycle. As tansy often grows in discrete clumps, the total population of C. graminis in an area may be divided and individuals may spend their entire life cycle within an area of a few square metres.
Adults mate between March and June. In the monitored populations at York, mating of the same pair could last over 24 hours, during which time some pairs moved between tansy patches. Mating in a Russian population of C. graminis is preceded by an elaborate ritual not evident in other populations of the species, involving the male tapping the female's eyes, pronotum and antennae with its antennae. Mated females lay batches of 3–15 elongated, yellow eggs (each 2 mm long) on the underside of the tansy leaves. Eggs hatch into grey larvae. In captivity, one newly mated female produced 561 eggs over 136 days and another produced 158 eggs over 49 days. Females will lay in several locations; the average clutch size is 5–6 eggs. Female C. graminis will cannibalise the eggs of other females. In laboratory conditions, newly hatched larvae have been shown to survive for at least four days without food and thus have a long window of opportunity in which to reach a tansy plant. In July, the final instar larvae burrow underground beneath the plant to pupate, although very little is known about the biology of this process in C. graminis. Between August and September, this new adult population emerges to feed before returning underground to overwinter in October; emergence of adults is from March to April the next year. Long-term monitoring has indicated that survival during winter hibernation is surprisingly high, as autumn and spring population sizes are very similar. This is despite annual winter flooding of the River Ouse, implying that overwintering individuals must be extremely tolerant of long periods of inundation and oxygen deprivation. Approximately 5% of overwintering adults do not emerge from the soil after the winter, but remain underground for the next year in a state of extended diapause and emerge in the following spring.
A few adult beetles may overlap between the spring and summer populations, but most adults from the earlier emergence die before the end of summer. Both adult and larval tansy beetles are unable to detect their host plant, or each other, at a distance, either by smell, sight or a combination of the two. Starvation is thus likely to be a major contributor to mortality when beetles wander away from their host and become lost.
